Inkjet printheads operate by ejecting a droplet of ink through a nozzle and onto a recording medium, such as a sheet of paper. When a number of nozzles are arranged in a pattern, such as one or more linear arrays, the properly sequenced ejection of ink from each nozzle causes characters or other images to be printed on the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The printhead is usually part of a disposable print cartridge containing a supply of ink, where the print cartridge is easily installed in and removed from the printer.
In one design of a thermal inkjet print cartridge, the print cartridge includes: 1) an ink reservoir and ink channels to supply ink proximate to each of the nozzles; 2) a nozzle plate in which the nozzles are formed in a certain pattern; and 3) a substrate attached to a bottom surface of the nozzle plate, where a series of thin film heaters are formed on the substrate, generally one below each nozzle. Each heater includes a thin film resistor and appropriate current leads. To print a single dot of ink, an electrical current from an external power supply is passed through a selected heater. The heater is ohmically heated, in turn superheating a thin layer of the adjacent ink. This results in explosive vaporization of the ink, causing a droplet of ink to be ejected through an associated nozzle onto the paper.
One example of this type of print cartridge is shown in FIG. 1 as print cartridge 10. Print cartridge 10 generally includes a body 12 which acts as an ink reservoir. Body 12 may have formed on it one or more projections, such as projection 13, to enable print cartridge 10 to be secured in place within an ink printer. The printhead portion 14 of print cartridge 10 includes a metal nozzle plate 16 (such as a gold-plated nickel nozzle member), which has two parallel arrays of nozzles 17 formed in it using conventional photolithographic techniques or other known techniques. Nozzle plate 16 is attached by an adhesive to an underlying substrate (not shown) which includes heater resistors paired with each of nozzles 17.
A flexible insulating tape 18 has formed on it a number of conductors which terminate in contact pads 20. The other ends of the conductors on tape 18 are connected, using tape automated bonding (TAB), to electrodes on the substrate.
When print cartridge 10 is properly installed in a moveable carriage of an inkjet printer, pads 20 contact corresponding electrodes on the inkjet printer which supply the energization signals to the various heater resistors on the substrate. When printing, the carriage scans print cartridge 10 across the width of a sheet of paper, and the paper is incrementally moved perpendicular to the direction of movement of print cartridge 10.
To assemble the combined prior art structure of tape 18, nozzle plate 16, and the underlying substrate, nozzle plate 16 is first aligned with and secured to the substrate such that the heater resistors on the substrate are aligned with the nozzles formed on the nozzle plate. This is a fairly time consuming process which requires specially designed and expensive machinery for dispensing a UV curable adhesive on the substrate, manipulating the nozzle plates and substrates, aligning them, and then adhesively securing the nozzle plates to the substrates by curing the UV curable adhesive sandwiched between nozzle plate 16 and the substrate.
After the step of aligning and securing nozzle plate 16 to the substrate, a conventional tape automated bonding (TAB) process, performed by a commercially available automated bonding machine, is then carried out to position electrodes on the substrate with respect to conductors formed on tape 18 and bond the conductors to the substrate electrodes.
What is needed is a method for manufacturing inkjet printheads which does not entail the use of specially designed equipment for dispensing a UV curable adhesive, manipulating nozzle plates and substrates, aligning them, and curing the adhesive but only entails using commercially available equipment.